The present invention relates to an object-lens driving device for an optical pickup installed in an optical recording and/or reproducing apparatus and, more particularly, to a device for supporting an object-lens driving portion, which elastically supports the object-lens driving portion according to vertical and/or horizontal displacement of the object-lens driving portion.
In a recording/reproducing apparatus employing an optical recording medium (hereinafter referred to as a disk) such as a laser disk player or compact disk player, an optical pickup having an object lens is provided for projecting a light beam (laser beam) onto the surface of the disk and detecting the reflected beam therefrom in order to read recorded digital data as a binary signal. In the operation of the optical pickup, the distance between the object lens and the disk must be kept constant to maintain correct focusing, and precise tracking of the projected light beam is required to reproduce the data on the disk without noise. Working against this, however, is the eccentricity error of the center hole of any manufactured optical disk, which is unavoidable. Once the disk is placed on a turntable, such eccentricity errors create unwanted oscillations in operation which cause reproduction errors. As a result, the distance between the optical disk and the object lens for the optical pickup cannot be kept constant and tracking on the disk is unstable. Therefore, to compensate for reproduction errors and achieve the correct focusing and tracking, a driving portion for slightly moving the object-lens - vertically and/or horizontallyxe2x80x94and some form of elastic support for supporting the driving portion are needed. Conventionally, a plurality of wires have been used as elastic supporting means in order to support the body of the driving portion having an object lens installed therein.
FIG. 1 illustrates a conventional optical pickup driving device employing wires as elastic supporting means.
As shown in FIG. 1, a fine pattern coil 4 is connected to a driving portion body 6 having an object lens 2 thereon. A plurality of wires 3 are provided, one end of each wire being connected to the fine pattern coil 4 and the other end thereof being inserted into a hole formed through a holder 1. The wires 3 serve to support the driving portion body 6.
In the above optical pickup driving device, when a drive current is applied through a power supply unit 7, the current flows to the fine pattern coil 4 via the wires 3. The current flowing through the fine pattern coil 4 and the magnetic force of a pair of magnets 5 and 5xe2x80x2 positioned orthogonal to the current direction of the fine pattern coil 4 generate an electromagnetic force in accordance with Fleming""s left-hand rule:
F=BIl sin(Bmxe2x8axa5Im)
where F is electromagnetic force, Bmxe2x8axa5Im is the angle between the magnetic force direction and the current direction, B is magnetic force, I is applied current, and l is the length of a conducting wire. Thus, the driving portion body 6 slightly moves depending on the direction of the electromagnetic force, with the wires 3 elastically biasing and supporting the driving portion body 6.
However, use of the wires 3 as a supporting member, which have a circular cross-section, is likely to result in a rolling phenomenon, since each inserted wire 3 makes contact with the holder 1, i.e., the inside of the hole 1a only, over a small surface area, and a gap exists between the hole 1a and the outer circumferential surface of the inserted wire 3. The rolling phenomenon is where the focus of the object lens 2 appears to rotate, not being constantly converged onto the disk (not shown) during the movement of the driving portion body 6 while being controlled for focusing and tracking, which is also the cause of reproduction errors.
The present invention is intended to overcome the above problems. An object of the present invention is to provide an object-lens driving device for increasing an area in which an elastic supporting member contacts a holder by using an elastic supporting plate member, so as to eliminate the rolling phenomenon.
To achieve the above object of the present invention, there is provided an object-lens driving device for an optical pickup, comprising a driving portion body having an object lens mounted thereon, an electromagnetic circuit attached to the driving portion body, including a fine pattern coil having a tracking coil and a focusing coil formed on a common plane, a supporting mechanism which supports the driving portion body, and a holder for mounting the supporting mechanism, wherein the supporting mechanism has a plurality of plate spring members, one end portion of each of said plate spring members being mounted to the holder, and an opposite end portion of each of said plate spring members being fixed to the driving portion body, for being elastically deformed either vertically or horizontally.
Many variations can be made according to the mechanism of combining the holder with the plate spring members: a plurality of vertical protrusions is extended from the holder, and a combining hole or groove is formed in each of the plate spring members, for receiving a corresponding one of the protrusions; alternatively, insertion holes are formed through the holder, for receiving the plate spring members, gaps between the holes and the plate spring members being filled with damping members. Each of the plate spring members may include a damping member for suppressing oscillations attached to one side thereof.